* Convert `SoftwareInterrupt` to a unit struct
* Remove the `SystemExt` trait and rename `SystemParts` to `SystemControl`
* Update all examples an HIL tests to reflect previous API changes
* Clean up imports in `hil-test` package, address `clippy` lint warnings
* Update `CHANGELOG.md`
* Create an `embedded-hal-02` feature and gate implementations, rename `eh1` to `embedded-hal`
* Use native `Delay` APIs in examples where applicable
* Fix example imports, be explicit about about `embedded-hal-02` feature requirements
* Update `CHANGELOG.md`